The Departments of Medicine (Division of Nephrology), Surgery, and Radiology, Duke University Medical Center and the Department of Internal Medicine, Wake-Forest University (subcontractor) are applying to continue their ongoing participation as a clinical center in the NI DDK-sponsored Dialysis Access Consortium (DAC) Clinical Trial. Surgical creation of a vascular access is necessary to permit chronic hemodialysis, which sustains the life of patients with end stage renal disease. These vascular accesses have a limited lifespan, and maintenance of a durable access is responsible for significant patient morbidity and expense. The DAC comprises two prospective, double blind, randomized controlled clinical trials examining means to prolong survival of hemodialysis vascular accesses. Patients undergoing placement of a native arteriovenous fistula are randomized to receive clopidogrel or placebo for the 6 weeks immediately following surgery. The primary endpoint is fistula patency at 6 weeks. The secondary endpoint is suitability for dialysis, as assessed within 4 months in patients already on dialysis and within one month of eventual commencement of dialysis in patients not yet on dialysis. Patients undergoing placement of a synthetic arteriovenous graft are randomized to receive Aggrenox (aspirin/persantine) or placebo from the time of graft placement until the primary endpoint, unassisted graft patency, is reached. Patients undergo ultrasonic graft flow monitoring when the graft is first used and monthly thereafter. If there are clinical indications, or if monitored graft flow drops significantly from baseline, patients are referred for angiography. If a greater than 50% stenosis is detected, angiographic dilatation is performed and the study endpoint is reached. Spontaneous graft clotting is also a study endpoint. DNA will be saved for all enrollees to permit ancillary studies examining potential genetic risk factors for shortened access survival. Relevance to Public Health: When a patient with kidney failure undergoes hemodialysis, blood is removed from the body, cleansed in a dialysis machine, and returned. The surgically created connection between an artery and a vein used to withdraw and return blood is of only limited reliability. This study is an attempt to reduce patient inconvenience and health care system expense by developing methods to prolong the lifespan of these connections.